Electrical measuring and energy control system



Oct. 17, 1950 J. L. MICHAELIS 2,526,496

ELECTRICAL MEASURING AND ENERGY CONTROL SYSTEM Filed NOV. 6, 1948 l l ll w n f 'HMI ll I L0 l J o I Q Q lillilllsl 3r (\l m x 3 3 3 m (0 a L (nlmuw I /x 2 a l a T K; 3 n2 INVENTOR- JOHN L. MlCHAELJS ATTORNEYPatented Oct. 17, 1950 OFFICE ELECTRICAL MEASURING AND ENERGY CONTROLSYSTEM John L. Michaelis, New Martinsville, W. Va.

Application November 6, 1948, Serial No. 58,675

l 3 Claims.

My invention relates to a control system or apparatus whereby a desirednormal condition is automatically maintained. in a simplified andimproved manner.

For example, the system may be used to control water temperature, ashereinafter described, and may also be used in various other ways,wherever a change from a normal or desired condition has the effect ofchanging the flow in an electrical measuring circuit such as that of athermocouple.

For example, such a circuit can be utilized to control the speed of amotor, or control mechanical forces or illumination, where changes insuch speed, forces, pressure or illumination produce a fluctuationincurrent. fiow in a control circuit. For example, piezo crystals can beused to produce a voltage proportional to a mechanical force orpressures, and there are photo-electric cells which will produce a D.C'. voltage proportional to the illumination on the surface of the cell.

Another object of my invention is to provide a control system of thecharacter referred to wherein a control circuit or a measuring andcontrol circuit that uses the null balance method,

by an appropriate measuring element, is employed to reach a desiredbalanced condition, there being three distinct voltages involved ineffecting such measurement and balance; i. e.

A. A pre-set adjustable (standard) voltage.

An unknown (variable) voltage that is to be measured and/ or controlled.

C. A correction voltage exactly equal (either additive or subtractive)to the difference between A and B above.

reference matic and schematic view showing the system I which I employ.

In this instance, the system is shown as controlling. the temperature ofwater in a tank, but

I it will be understood that, as above indicated,

another control circuit subject to changes in physical condition that isto be controlled can be substituted for the thermocouple circuit 22.

The numeral 2 represents wires supplied with D. C. current from asuitable source. These wires, together with conductors 3 and 4, supplycurrent to a reversible motor 5 that is here shown as employed foropening and closing a valve 6 that admits steam to a tank 1 whichcontains water whose temperature is to be maintained at say 160 F., thewater level being automatically maintained by a float-actuated valve 8,as water is drawn oiT through a pipe 9.

Conductors I0 and II have connection with coil I2 of an autotransformer13. This transformer has a pointer 14 that is automatically moved backand forth along the coil 12 by a motor 3| or a motor 34 and therebyproduces a voltage that is impressed on the primary winding of atransformer H5. The primary coil of IE is fixedly connected at 49, tothe transformer A manually-set slide contact 50 and conductor l0 impressa desired voltage on the primary winding of a 110/110 volt transformerI5, which voltage is thus manually set for a pre-determined desiredconstant control value. 1

The voltage in the secondary circuit ll of the secondary windings and acopper oxide rectifier i8 is thereby changed, as conditions may vary. Anammeter I9 is provided in the D. C.-circuit 20 of this rectifier, and aresistor 21 is in this circuit. It is through changes in voltage acrossthis resistor that the operations of the system are controlled. Changesin this voltage are primarily effected through changes of temperature inthe tank I and hence current flow inthe thermocouplev circuit 22. 1

A null balance voltage circuit is actuated by any voltage unbalancebetween the thermocouple circuit 22 and voltage across resistor 2|. Anyvoltage unbalance will actuate a switch arm. or needle 23 in agalvanometer 24. The voltage produced across resistor 2| will bechanged, as hereinafter explained, as a result of a movement of pointer14, such that a balance is always effected between thermocouple voltage22 and the voltage across resistor 21:.

In a typical control application such as tha shown in the drawing, theprimary of the autotransformer I6 is connected to the 25-volt primarywinding tap- With 1000 ohms resistance at 2| and a tap at .0503 ohm, theammeter I9 will be caused to show a reading of mill-iamperes, resistortap voltage of 5.03 millivolts, ata temperature of 200 F.

Assuming that is is desired to maintain the temperature of the water inthe tank I at 160 F. and that there is a constant fiow out of the tank,through the pipe 9, the steam valve 6 will be maintained in a partlyopened position to supply the required quantity of steam to maintainthis temperature. The manually-set slide contact member 50 is sopositioned that the secondary voltage produced by the transformer I is76 volts. Thus this 76 volt potential in circuit I! is the desiredconstant point. When the autotransformer pointer I4 will be at themidpoint and at this 160 F. temperature, the ammeter I9 will register'76 milliamperes. The galvanometer needle 23 will be at the midpoint andthe relay switches at 25 and 26 deenergized.

If the demand at the tank I suddenly increases, or the steam pressuredrops, the temperature in the tank will drop. Assuming that thetemperature drops F., which results in a 6% change in the full scalereading of the instrument, the voltage produced by the thermocouple willdrop and cause a current to flow through the galvanometer 24, as thevoltage produced at the resistor 2| equals 3.81 millivolts, and thethermocouple produces 3.50 millivolts, at 150 F. The galvanometer needle23 engages the contact member 21, thus short circuiting a resistor 28,which reduces the bias in the tube 29, to conduct current and energizethe relay switch 25.

Closing of the relay switch completes the circuit through the motor 5 toeffect opening of the steam valve and also simultaneously completes thecircuit through the motor 3| to effect a change in the voltage atresistor 2 I, so that the galvanometer will return to zero or balance.

In order to effect or permit the return of the galvanometer to zeroposition, the current through the resistor 2| must be changed from '76milliamperes to 70 milliamperes; .O'76 .0503 equals 3.81 millivoltsequals 160 F., and .0'70 .0503 equals 3.50 millivolts equals 150 F.

'The voltage across the resistor 2| must change from 76 volts to 70volts. The voltage supplied by the transformer I6 is 76 volts. This 76volt output of transformer I5 determines the control point. In thisdescription, it is assumed there is no energy lost through the changefrom A. C. to D. C., at the copper oxide rectifier. There will actuallybe some slight losses, but the fundamental operation and theory isunchanged.

If the voltage across the resistor 2| is to be changed from '76 volts to70 volts to effect a voltage balance, and the voltage output of thetransformer I5 is constant at '76, then a subtractive voltage of sixvolts must :be produced by the transformer I 6. This six volts potentialis generated by a movement of the pointer I4 as a result of the motor 3|being energized by relay switch 25, as described above. The voltageratio of the transformer I6 is /50. Therefore, a threevolt change isrequired in the primary of transformer I6 to produce a six volt changein circuit The motor 3| will effect a change of 50 volts in 60 seconds,or /6 volt per second. To effect a change of three volts, 3.6 secondsare therefore required. In 3.6 seconds, the voltage across the resistor2| will change from 76 volts to 70 volts,

and this, in turn, will cause the tap voltage at 2| to balance thethermocouple voltage. With zero voltage difference, the galvanometer 24will return to zero as shown on the drawing. The short circuit of theresistor 28 is therefore removed and the bias is then on the vacuum tube29. The

relay switch at 25 is therefore deenergized and the motors 5 and 3|stopped.

During the rebalance of the voltage across the resistor 2|, the motor 5was running for 3.6 seconds, and the valve 6 will have been moved forapproximately 3% of its total travel. Thus for a 6% change (of fullinstrument range) of the temperature under measurement, the steamsupplyvalve 6 will be moved 3%. By changing the speed of the motor 3|, withrespect to the motor 5 and/or changing the primary tap of thetransformer I6, any throttling range can be obtained to suit theparticular control application.

The above description is for an application that requires 200%throttling range. This is defined as a operator or valve movement withrespect to a 100% change of the voltage under measurement. Forparticular types of application, it is desirable that the throttlingrange be for example 300%. To design a control system that will permitready and convenient change of the throttling range is a practicalrequirement.

This change in response or throttling range is necessary to obtainstability of the system under control. In some applications in orderthat the system is stable and will not hunt, it is necessary that thecorrective energy level be changed at a very slow rate. In othersystems, it is desired that the correction be made as rapidly aspossible, but in all cases, it is desired that the rate of correction beas rapid as the stability of the system will permit and this requiresreadily adjustable means for changing the rate of response of thecorrective energy level with respect to the change in the variablevoltage under measurement.

The system herein proposed can accomplish a flexible adjustment of thethrottling range for the ratio of response of movement of the remoteoperator (motor 5) with respect to the rate of re balancing of thevoltage under measurement (by the motor 3 I), by changing the rate atwhich the correction voltage is produced through movement of the motor 3I. This can be done by chang ing the transformer tap at I6 or bychanging the gear ratio of motor 3| (gears 363|), or by changing thegear ratio between the motor 5 and the valve 6.

To compensate for control point shift that is caused by load change, anautomatic reset circuit is included. As soon as the pointer I4 of thetransformer I3 has been moved in one direction from its neutral point,or at any time the thermocouple circuit 22 is not exactly 3.31millivolts, a switch at 33 is closed to start a motor 34. The motor 34through a shaft 35, gearing 36 and 31 and a shaft 38 will drive thepointer I4 back to the neutral point. The frame of the motor 3| ismounted on the gear 31. This motor 34, when it runs, has the same effectas motor 3| except its effect is governed by the gear ratio of gears 36and 37 and the final result is slow movement of the shaft 38 and pointerI4. The motor 3| is equipped w th flexible pigtail electricalconnections. This changes the voltage at the transformer I6 which, inturn, causes change in the voltage at resistor 2|. These changes willresult in again unbalancing of the galvanometer to effect closing of thecircuit through the switches 25 or 26 and thereby again effect operationof the motors 5 and 3|. This control movement caused by the motor 34will result in movement of the steam valve motor 5 at a rate equal tothe following: voltage on the primary winding of the transformer I 6equal +50 or volt per minute of running. This volt per minute could bebalanced by the motor 3| running one second. Whenever the motor 3| is inoperation, the motor 5 is also energized. This one second of movementwill represent .8 valve moment.

Thus after temperature in the tank changes from 160 F. to 150 F., thesteam valve is opened for 3.6 seconds or 3% additional opening. Everyone minute thereafter, the valve is moved .8% until the temperaturereturns to the control point or the voltage output of transformer l6equals zero. The reset control is adjustable in magnitude by changingthe speed or the gear ratio of the motor 34, and/or the gear ratio ofgears 36 and 31.

If now, the temperature increases above the desired 160 F., the changein voltage by the thermocouple will be such as to cause the galvanometerneedle 23 to close the circuit at contact member 39, thus closing themagneticallyoperated switch 26 and effecting reversal of the motor 5, toreduce the steam supply, and also reversing the motor 3|, for movementof the pointer l4 in the opposite direction.

The switches 33 and 40 are operated by a tooth 4| on a cam disc 42, thatis secured to the shaft 38. The switch at 33 will be closed whenever thecam tooth has been rotated to the right of the vertical mid point, orwhenever the pointer I4 is above its mid point. The switch 40 will beclosed whenever the cam tooth has been rotated to the left of thevertical mid line and the pointer I4 is below its mid point. When thecam tooth 4| is at the vertical mid point as shown on the drawing, bothswitches 33-40 are open.

The cam 42 also operates limit switches at 44 and 45. When the pointerI4 is at approximately 135 degrees below its neutral point, at one side,the cam tooth 4| will open the switch 44, to stop operation of themotors 5, 3| and 34 in a given direction. When the pointer is moved 135degrees to the opposite direction, the switch 45 will be opened toprevent further operation of the motors 5, 3| and 34 in the otherdirection.

Since either the switch 33 or the switch 40 is closed at such time, themotor 34 will be energized in a direction to restore the pointer M toits neutral position and the switches 33, 40, 44 and 45 to their normalpositions shown in the drawing.

While the motors are shown as wired for D. C. current, it will beunderstood that A. C. motors can be used in the system.

I claim as my invention:

1. An electrical control system comprising a null balance circuit, formeasuring an electric potential and controlling an energy level at aspecific point where the electric potential is generated proportional tothat energy level, a potentiometer for the nullcircuit, an electricmotor that is automatically operated through changes in the saidvoltage, to operate the potentiometer and maintain; a voltage balance inthe null balance circuit, a second motor controlled by the first-namedmotor and operable to effect a change in the degree of energy manifestedat the said point, means for changing the extent of movement of thesecond named motor with respect to a given percent change in the voltagebeing measured, a variable ratio transformer for varying the potentialproduced in the null balance circuit per increment of motion of the po-6 tentiometer slider, to effect any desired duration or percentage ofmovement of the second-named motor for a given percentage of change inthe potential undergoing measurement.

2. An electrical control system comprising an electrical measuringcircuit, means for producing therein a potential that is proportional toenergy that is manifested at a given location and is subject tofluctuations through changes from a predetermined energy level at thespecific location, an electrically-responsive switch movable in eitherof two directions from the neutral position, in response to fluctuationsin said circuit, a control circuit closed by the switch when moved inone direction through decrease of energy from said level, a secondcontrol circuit closed by the switch when moved in the oppositedirection upon increase of energy above said level, a reversible motorcontrolled for movement in opposite directions by the respective controlcircuits, a null balance system for the measuring circuit, apotentiometer slider movable from its normal position by said motor, tobring the potential undergoing measurement and the measuring circuitinto null balance and thereby restore the switch to its neutralposition, a second reversible motor, whose direction and duration ofrotation is controlled by the said measuring circuit, in response tosaid fluctuations from a predetermined energy level at the saidlocation, and serving to effect increase or decrease in the degree ofenergy manifested at said location, and thus effect restoration of thepredetermined energy level, a third reversible electric motor for movingthe potentiometer slider, in either direction, to effect unbalance ofthe null system relative to the measuring circuit, a pair of switchesrespectively controlling the direction of movement of the third motor,so that the third-named motor is energized at any time that thefluctuating potential that is undergoing measurement differs from thepredetermined desired valve, to thereby effect return of thepotentiometer slider, to its normal position, and means associated withthe potentiometer slider, for closing one of these switches when theslider is moved in one direction and for closing the other switch whenthe slider is moved in the opposite direction, the said means servingalso to open both of these last-named switches when the slider reachesits normal or neutral mid position, thereby placing the system incondition for successive repeat operations for so long as said energy isin excess of or less than said level.

3. A control system as recited in claim 2, wherein the potentiometerslider is returned to its said normal or'original position at a slowrate relative to the speed at which it has been moved by the first-namedmotor.

JOHN L. NIICHAELIS.

Name Date Lilja gvgvfiuflv Mar. 9, 1943 Number

